Extracorporeal blood processing systems remove blood from a patient's body, process the blood for some purpose and return it to the body. One type of extracorporeal blood processing is an apheresis procedure in which blood from a donor is directed to a blood component separation device (e.g., centrifuge). The blood is separated into various blood component types (e.g., red blood cells, white blood cells, platelets, plasma) for collection or therapeutic purposes while the remainder are returned to the donor. Apheresis procedures are often conducted at clinics with multiple donors being processed on a single apheresis machine in a single day. Another type of extracorporeal blood processing is an oxygenation procedure in which blood is removed from a patient, directed to a blood oxygenation device where the blood is oxygenated and returned to the patient. This blood procedure is useful in ensuring that freshly oxygenated blood is circulated to the patient during surgery when the heart and lungs are stopped. Other extracorporeal blood processing techniques, such as hemodialysis, blood salvage and blood washing are also well-known.
In extracorporeal systems, such as those mentioned above, positive and negative pressures must be accurately monitored as blood is removed from and returned to the patient. In addition, it is highly desirable for blood processing systems to use a disposable assembly for any portion of the system which contacts the blood. For such systems, the mechanism for monitoring pressure must be capable of connecting with and monitoring blood pressure in the disposable assembly.
In previous blood processing systems, pressure has been measured using a pressure sensor in communication with a blood conduit. In one such embodiment, a diaphragm is incorporated into the blood conduit, and blood, in the conduit, contacts one surface of the diaphragm while a captive air space is in contact with a second surface of the diaphragm. A pressure sensor communicates with the captive air space. In addition, the pressure sensor measures the pressure changes in the captive air space as the diaphragm flexes in response to the pressure changes in the blood conduit. Such a system is not entirely satisfactory. If an air leak develops in the captive air space, the sensor is not capable of accurately measuring pressure in the blood conduit. In another blood processing system, pressure in a blood conduit has been measured by a force sensor placed around the blood conduit. To determine the pressure of the blood within the conduit, the force sensor measures the expansion of the blood conduit. These pressure monitoring systems have been known to produce less than accurate pressure measurements, especially for negative pressures.
A need, therefore, exists for a blood processing system having a sensor that is capable of measuring positive and negative pressure of a fluid flowing through a conduit. Such a system should be suitable for use in measuring pressures within a disposable assembly, and the sensor should be capable of being removably coupled with the disposable assembly. Moreover, such a system should avoid the durability problems associated with pressure measuring systems using captive air spaces.